The invention relates to a method for directly deriving amplitude and phase information of an object as an electron wave function formed by means of a number of object images recorded with a high-resolution electron microscope, said images being recorded in image planes with slightly different defocus values.
The invention also relates to a high-resolution electron microscope suitable for performing a method in accordance with the invention.
A method of the kind set forth is known from the publication "A new procedure for wave function restoration in high-resolution electron microscopy" by D. Van Dyck and W. Coene in Optik 77, No. 3 (1987), pp. 125-128. The method described therein is based on the intensity of an image and the derivative thereof for a selected defocus value. In practice a number of images are preferably recorded in a limited number of image planes with defocus values in the range of the selected defocus value which deviate only little from one another. Such a gradient method is rather cumbersome and utilizes exclusively information from microscope images around the selected defocus value. Moreover, the defocus step required between two images to be recorded in order to ensure suitable execution of the method is too small to be feasible in contemporary high-resolution electron microscopes. Moreover, this method is too susceptible to the presence of noise in the experimental images.